Instant Notes - Key concepts

1.4. Mosaic and Regulative development

Based on classical studies of experimental embryology, embryo development was broadly divided into two categories: Regulative (classically associated to Vertebrates) and Mosaic (classically associated to Invertebrates). It is now clear that the development of all embryos involves a combination of both mechanisms. 

Mosaic development: if development was exclusively controlled by cytoplasmic determinants, the fate of every cell would depend uniquely on its lineage, while its position in the embryo would be totally irrelevant.  Thus, in "mosaic embryo" (which is an abstraction) the fate of the cell is governed entirely by its intrinsic characteristics, i.e. cytoplasmic determinants it inherits at cell division. In this scenario, each cell undergoes autonomous specification. If the cells are removed from the embryo they should, in principle, develop according to their intrinsic instructions and differentiate into the appropriate part of the embryo even if the rest of the embryo is not there. 

Regulative Development:  if development was controlled exclusively by inductive signals, the fate of every cell would depend mostly on its position in the embryo. The fate of the cell is governed  by its interactions with other cells. Each cell is said to undergo conditional specification. If the cells are removed from the embryo they should not fulfill their normal fate because they lack the necessary interactions. 

(think about what would be the relationship between cell potency and cell fate in a condition of Mosaic development versus Regulative development)